Memory card is an electronic flash memory data storage device used for storing digital information. Memory cards are commonly used in many electronic devices, such as digital cameras, mobile phones, laptop computers, MP3 players, and video game consoles. One popular type of memory cards is secure digital (SD) cards. SD cards are small and light, and are suitable as data storage in portable electronic devices.
Some electronic devices operate with two or more memory cards. For example, in some high end digital camera, two memory cards are presented. One memory card is used for storing raw image file which contains the unprocessed data from the sensor, and other memory card is used for storing compressed JPEG files. FIG. 1 shows a conventional electronic device 100 that operates two SD cards. The electronic device 100 includes a first host controller 102 for operating a first SD card 114, and a second host controller 104 for operating a second SD card 116. The first host controller 102 powers the first SD card 114 via a first power line 106. A first data bus 110 is coupled between the first host controller 102 and the first SD card 114 for transmitting data between the first host controller 104 and the first SD card 114. Similarly, the second host controller 104 powers the second SD card 116 via a second power line 108. A second data bus 112 is coupled between the second host controller 104 and the second SD card 116 for transmitting data between the second host controller 104 and the second SD card 116. One drawback of this conventional electronic device 100 is that two individual host controllers are needed in order to operate two SD cards respectively, and thus the cost is increased.